Preparation of solid ammonium glyphosate using organic solvent in extraction

ABSTRACT

A method of preparing ammonium glyphosate suitable for preparation of water-soluble solid ammonium glyphosate formulation by an extraction with organic solvent in a gas-liquid-solid phase system, which comprises adding glyphosate and water into a reactor with a stirer, introducing ammonia to carry out the reaction, an aqueous solution of ammonium glyphosate is formed after the reaction is completed; adding a water-soluble organic solvent such as methanol and/or ethanol and/or methylal to decrease the solubility of the ammonium glyphosate in the system, thereby crystallizing out ammonium glyphosate; and filtering in suction or further oven-drying to obtain the solid ammonium glyphosate. The organic solvent may be recovered and reused by rectifying or distilling, the remainder residue may be returned to the reaction procedure or used in the preparation of the aqueous formulation of ammonium glyphosate.

FIELD OF THE INVENTION

The present invention relates to a process for preparing solid ammoniumglyphosate, more particularly to a process for preparing solid ammoniumglyphosate useful in the preparation of a water-soluble solidformulation of ammonium glyphosate by the reaction in a gas-liquid-solidphase system and the extraction with an organic solvent.

BACKGROUND OF THE INVENTION

The chemical name of glyphosate is N-phosphonomethyl glycine, which hasthe following molecular formula.

Glyphosate is a broad-spectrum sterile herbicide highly effective in theprevention and control of various malignant deep-rooted weeds due togood systemic conduction performance. Recently, its sales volume isgradually increased. The application field thereof is further extendedwith the gradual popularization of glyphosate-resisting transgenosiscrops. Now, it has become a herbicide with the highest sales volume andthe quickest speed increased in its production in the world.

Because the solubility of glyphosate in water is very low (1.2 g per 100g water at 25° C.), as for practical application, the glyphosate isusually processed into water-soluble salts, and is commerciallyavailable as an aqueous formulation of glyphosate isopropylamine salt,an aqueous formulation of glyphosate trimesium, an aqueous formulationor a water-soluble powder (granula) of ammonium (sodium) glyphosate.Because the aqueous formulation of glyphosate salt contains a greatamount of water as a solvent and its package has an increased weight andvolume, the water-soluble solid formulation has a relatively low cost.As for the end users, the products with lower price and betterperformance are required. It is obvious that the water-soluble solidformulation of ammonium glyphosate is more competitive than the aqueousformulation thereof.

Chinese Patent Application No. CN-96196134.1, which was published onSep. 9, 1998 and was issued to Monsanto Company of American on Jul. 18,2001, shows that great efforts have been made for the preparation anduse of compositions of dry glyphosate formulation, and for relatedmethods. Herein, the related patents and references are used as thereferences for the present invention. The patent discloses a process forpreparing ammonium glyphosate by the reaction of an aqueous ammoniumhydroxide solution (ammonia water) with glyphosate in a liquid-solidreaction system. Since the concentration of ammonia water is only 29%,namely, it contains a large amount of water, continuous drying isrequired so as to keep an appropriate water content during the process.Further, the rate for introducing ammonia water is required to controlstrictly so as to ensure the rate for introducing water into the systemless than that for removing it from the system during the reaction. Thewater content should be periodically measured, and the product should bedried and then pulverized. Furthermore, sodium sulfite as an antioxidant(oxidation inhibitor) is required further to add during the reaction inorder to decrease the oxidization of glyphosate by hot air because theoxidation causes formation nitrosamine which content needs to becontrolled. Therefore, the technology and control are relativelycomplicated to some extent, and a large amount of water has to beremoved by hot wind, so the energy consumption is higher.

Chinese Patent Application No. CN-96196133.3, which was published onSep. 9, 1998 and was grant on Jul. 4, 2001, discloses a process forpreparing ammonium glyphosate by the reaction of glyphosate andanhydrous ammonia. The process needs to use a “self-cleaning type” ofautoclave equipped a “propeller” which has a precision dimension and isable to scrape continuously the products deposited on the reactor wall,otherwise, the solid deposition formed will affect the removal ofreaction heat. Furthermore, the rate for introducing ammonia is strictlycontrolled in order to ensure introducing the ammonia and glyphosateinto the reactor in a manner that they are completely homogeneousdispersed. If the inlet for ammonia is not set in an appropriateposition, fouling and clogging will easily occur at the inlet and solidaggregations will also be formed. The disadvantages of the process arethat it is difficult to removal the reaction heat from the gas-solidreaction system and the reaction rate is slow.

Chinese Patent Application No. CN-99119971.5, which was published onJul. 19, 2000 and was grant on Oct. 10, 2001, discloses a commercialprocess for preparing ammonium glyphosate by the reaction of glyphosatewith liquid ammonia. Because the process is carried out directly throughthe liquid-solid reaction of liquid ammonia with glyphosate, it isrequired to be carried out under a pressure of 1.0-2.8 MPa while thereaction heat is required to remove timely during the reaction to avoidresulting in danger under too high pressure. The process hasdisadvantages in that the reaction has to be conducted at a higherpressure and bigger equipment is further required to install forrecovering ammonia.

Although the aforementioned inventions provide the process for preparingdry ammonium glyphosate salt that can be used in the preparation of thewater-soluble solid formulation, the processes suffer from deficienciessuch as slow reaction rate, high cost or complicated technology and thelike. That is, the prior arts are such unsatisfactory that there isstill a need for a further invention. In this regard, the presentinvention solves the problems associated with the process in the priorarts and meets requirements that are not yet realized in aforementionedinventions or well-know technologies.

DISCLOSURE OF THE PRESENT INVENTION

An object of the present invention is to overcome the deficienciesassociated with the process in the prior arts and provide a novelprocess for preparing ammonium glyphosate that can be used in thepreparation of the water-soluble solid formulation by the extractionwith an organic solvent.

Another object of the present invention is to provide an easilyindustrialized process for preparing ammonium glyphosate.

These and other objects of the present invention are further illustratedin detail by the following description.

The present invention provides a process for preparing solid ammoniumglyphosate by the reaction in a gas-liquid-solid phase system, whichcomprises adding glyphosate and water into a normal reactor, introducingammonia to carry out the reaction, an aqueous solution of ammoniumglyphosate is formed after the reaction is completed; adding an organicsolvent with a relatively high solubility in water to decrease thesolubility of the ammonium glyphosate in the system, therebycrystallizing out ammonium glyphosate, and filtering in suction toobtain the solid ammonium glyphosate. The organic solvent recovered byrectifying or distilling the mother liquor may be reused, the remainderresidue may be returned to the reaction procedure or used in thepreparation of the aqueous formulation of ammonium glyphosate.

Powder of crystalline ammonium glyphosate is obtained in a simple methodby reacting glyphosate with ammonia (or ammonia water) in aqueous phaseand adding an organic solvent after the reaction is finished to decreasethe solubility of ammonium glyphosate in the system. Therefore, adesired and easily industrialized process is provided for preparingammonium glyphosate salt that is useful in the preparation of aherbicide composition of water-soluble solid ammonium glyphosate salt.

The ammonium glyphosate is present in a formula as the following:

Wherein m is a positive integer from 1 to 3, the ammonium cation maylink to the hydroxyl which is bonded with a carbonyl or a phosphoryl. Asfor the single molecule, m equals 1-3. The generally used ammoniumglyphosate salt is a mono-ammonium salt, namely, m equals 1. However, itmay not be deemed simply that the ammonium glyphosate salt obtained inpractical production has m just equal to a positive integer, but a valuein the range of 0.8-1.3. These substances have very high solubility inwater and the concentration of their aqueous solutions may be more than20% at room temperature. However, they have very low solubility in suchorganic solvents that are completely miscible with any proportion ofwater or have a relatively high solubility in water. Thus, after thereaction is ended, such organic solvent(s) is(are) added to the reactionsolution to form a homogeneous solution with water in the system,thereby substantially decreasing the solubility of the ammoniumglyphosate salt therein and crystallizing the salt out. Such solventsmay include, or may be, alcohols and acetals, etc. or a mixture of twoor more solvents. The alcohols may include monobase alcohols having 1-4carbon atoms. It is preferred to use methanol, ethanol, propanol,butanol and methylal in terms of cost effective, which can be used aloneor as a mixture of thereof. It is not recommended to use the organicsolvent having a lower solubility in water, such as aliphatichydrocarbon, aromatic hydrocarbon and ethers and the like. Such solventsare not able to form a stable homogeneous phase in water and cannoteffectively isolat ammonium glyphosate salt since said salt dissolved inthe aqueous layer after phase separation. Certainly, if the organicsolvent which is used is mixed with a little amount (for, example, lessthan 5%) of organic or inorganic substances that are not selected in thepresent invention, such as, aliphatic hydrocarbon, aromatic hydrocarbon,ethers and the like, there will be no effect on the realization of theprocess according to the present invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is the schematic view of the process according to the presentinvention.

Methanol as an example is used to describe specifically the presentinvention. The present invention can be carried out with ethanol,methylal and other solvents that are suitable for the requirement of theprocess in a manner similar to methanol. The invention is intended tocover various modification that the solvents not listed in the presentinvention are used and that the operation parameters of the process areadjusted.

The embodiment according to the present invention is to obtain solidammonium glyphosate by adding an appropriate amount of water to anautoclave equipped with a stirrer; adding once or in portions a crudeglyphosate powder in an amount 0.2-2 times as that of the water byweight, wherein the crude glyphosate powder may be a 95% or more than90% solid glyphosate that has been dried, or an undried glyphosatehaving 5-20% water content; then stirring for 5-30 minutes; subsequentlyintroducing gaseous ammonia at a controlled temperature 30-100° C. tocarry out the reaction for 0.5-3 hrs; stop inletting ammonia when thesolution becomes clear and transparent; cooling the reaction solution toless than 30° C.; and then filtering.

The amount of gaseous ammonia introduced is 1.01-1.5 times by mole asthat of glyphosate added. When the ammonia is not enough, the reactionwill not be carried out completely to cause the product havingrelatively more glyphosate, and thus a part of the water-soluble solidammonium glyphosate may not be dissolved due to very low the solubilityof glyphosate in water. If the ammonia is introduced in excess,relatively more free ammonia will remain in the system, thereby theammonia will escape in subsequent processes to result in theenvironmental pollution. A relatively simple method for judging the endpoint of the reaction is to measure the pH of the reaction system. Theinventor believes that the pH should be kept at 5-8. The solubility ofammonium glyphosate varies with the concentration of the aqueousmethanol solution, the higher the concentration of aqueous methanolsolution is, the lower the solubility of ammonium glyphosate is. Thesaturation concentrations of ammonium glyphosate in differentconcentrations of the aqueous methanol solution at 30° C. are listed inTable 1.

TABLE 1 The saturation concentrations of ammonium glyphosate indifferent aqueous methanol solutions. Content of methanol (w/w) % 5 2040 60 80 100 Saturation 18.2 8.9 4.3 1.5 0.9 0.6 concentration (w/w) %

Although the solubility of ammonium glyphosate is lower in the higherconcentration of aqueous methanol solution, when methanol is added toomuch (e.g. the ratio of methanol to water is higher than 10:1) and theamount of mother liquor is thus increased too high, on the contrary, thetotal amount of ammonium glyphosate dissolved in the mother liquor isincreased and the utilization of the equipment is decreased.

The methanol used in the process can be recovered for reuse. Afterfiltered, the mother liquor containing methanol, water, ammoniumglyphosate, free ammonia, glyphosate and impurities is rectified torecover the methanol which is used for the crystallization andseparation. After recovering methanol, the bottom residue containing2-8% of the ammonium glyphosate may be returned to the synthesis processfor the preparation of ammonium glyphosate, or used for the preparationof aqueous formulation of ammonium glyphosate by increasing the contentof ammonium glyphosate therein and adding surfactants.

In the process according to the present invention, since the formationof nitrosamine which content needs to be controlled is substantiallyreduced due to reducing significantly the heat load for oven-drying,sodium sulfite as an antioxidant is not necessarily added during thewhole reaction.

There is not particular limit to the methanol used for thecrystallization and separation in the present invention, which may beindustrial grade methanol of 98% by weight or recovered methanol of 90%by weight. So in the recovery process of methanol according to thepresent invention a simple distillation plant may be used withoutconsumption of a great amount of steam to obtain a high content ofmethanol. In the present invention system, the mole ratio of methanol towater is 1-10:1, and preferred is 2-5:1.

The ammonium glyphosate salt obtained according to the process of thepresent invention can be directly used for preparing the solidformulation of ammonium glyphosate salt because of lower water content,and also can be dried in various manners such as pneumatic drying oroven-drying and the like without any agglomerate. The water content ororganic solvent content in the ammonium glyphosate salt can be reducedto 0.1 -2% by oven drying.

The process for preparing the solid ammonium glyphosate salt accordingto the present invention is simple in methodology and low in cost, andthe product has crystalline powder appearance after drying and is easilyto be made into the water-soluble solid formulation.

All the raw materials, aids and additives used in the present inventionare available from market.

The present invention is further illustrated by following specificexamples that are only used to illustrate the present invention, but notlimit the scope of the present invention. Unless otherwise specified,all the quantities, parts or percentages in the present invention areexpressed by weight.

Specific Modes for Practicing the Invention EXAMPLE 1

100 g of water and 120 g of the crude glyphosate powder (with a purityof 95%) were added once into a 2 L autoclave equipped with a stirrer anda thermometer. Ammonia was introduced in molar quantities 1.01 times asthat of the net glyphosate used in the autoclave under stirring to carryout the reaction. The reaction temperature was controlled at 35±5° C.When the pH reached 5 as an end point after the reaction lasted for 3hrs, the introduction of ammonia was ceased, and then the aqueousammonium glyphosate solution was cooled to the temperature of 25±5° C.under stirring. 100 g of methanol was then added for thecrystallization. The resulting crystals were filtered in suction fromthe system, and then dried to obtain the product of ammonium glyphosate.

EXAMPLE 2

The experiment process and equipment were the same as those inExample 1. Ammonia was introduced in molar quantities 1.2 times as thatof the net glyphosate used under stirring to carry out the reaction, Thereaction temperature was controlled at 70±5° C. When the pH reached 6.5as an end point after the reaction lasted for 2 hrs, the introduction ofammonia was ceased. The aqueous ammonium glyphosate solution was cooledto the temperature of 25±5° C. under stirring. After the reaction, 225 gof methanol was added for the crystallization, and the resultingcrystals were filtered in suction from the system, and then dried toobtain the product of ammonium glyphosate.

EXAMPLE 3

The experiment process and equipment were the same as those inExample 1. Ammonia was introduced in molar quantities 1.5 times as thatof the net glyphosate used under stirring to carry out the reaction, Thereaction temperature was controlled at 95±5° C. When the pH reached 6.5as an end point after the reaction lasted for 1 hr, the introduction ofammonia was ceased. The aqueous ammonium glyphosate solution was cooledto the temperature of 25±5° C. under stirring. After the reaction, 450 gof methanol was added for the crystallization, and the resultingcrystals were filtered in suction from the system and then dried toobtain the product of ammonium glyphosate.

EXAMPLE 4

The experiment process, equipment and reaction conditions were the sameas those in Example 2, except that 675 g of methanol was added for thecrystallization after the reaction.

EXAMPLE 5

The experiment process, equipment and reaction conditions were the sameas those in Example 2, except that 900 g of methanol was added for thecrystallization after the reaction.

EXAMPLE 6

The experiment process, equipment and reaction conditions were the sameas those in Example 2, except that 1000 g of methanol was added for thecrystallization after the reaction.

EXAMPLE 7

The experiment process, equipment and reaction conditions were the sameas those in Example 3, except that 450 g of ethanol was added after thereaction.

EXAMPLE 8

The experiment process, equipment and reaction conditions were the sameas those in Example 3, except that 450 g of methylal was added after thereaction.

EXAMPLE 9

The experiment process, equipment and reaction conditions were the sameas those in Example 3, except that the solvent (450 g) used for thecrystallization was consisted of methanol (65% by weight), methylal (25%by weight) and water (10% by weight).

EXAMPLE 10

The mother liquors obtained from Examples 1-6 by filtering weredistilled to obtain the methanol (A) having a 95 wt % of content and theaqueous solution (B) containing 5.1 wt % of ammonium glyphosate,respectively. The process of Example 1 was carried out with 100 g of thewet glyphosate powder (8% of water content) and 100 g of B, except that400 g A was added as the solvent.

EXAMPLE 11

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that 450 g solvent (consisting of 50%methanol and 50% ethanol) was used for the crystallization.

EXAMPLE 12

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that the solvent used for thecrystallization was 450 g of n-propanol.

EXAMPLE 13

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that the solvent used for thecrystallization was 450 g of n-butanol.

EXAMPLE 14

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that 550 g solvent (consisting of 50%methanol, 30% ethanol, 10% iso-propanol and 10% tert-butanol) was usedfor the crystallization.

EXAMPLE 15

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that 450 g solvent (consisting of 30%methanol, 50% ethanol, 20% methylal) was used for the crystallization.

EXAMPLE 16

The experiment process, equipment and reaction conditions were the sameas those in Example 3, except that 680 g of ethanol was added after thereaction.

EXAMPLE 17

The experiment process, equipment and reaction conditions were the sameas those in Example 2, except that 750 g of methylal was added after thereaction.

EXAMPLE 18

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that the solvent used for thecrystallization was 350 g of n-propanol.

EXAMPLE 19

The experiment process, equipment and reaction conditions were the sameas those in Example 9, except that the solvent used for thecrystallization was 400 g of n-butanol.

EXAMPLE 20

6.4 g of ammonium glyphosate was added to 100 g of II (containing 5.1%of ammonium glyphosate), then 8 g of EF8108 (produced by the ResearchInstitute of Jinling Petrochemical Corporation of SINOPEC) was furtheradded after dissolved under stirring. The resulting mixture was thenmixed homogeneously to obtain a clear and transparent product having thesame drug effect as that of aqueous formulation of 10% glyphosateavailable from market.

The purity and yield of product in each Example mentioned above areshown in Table 2 below, wherein the yields are calculated on the basisof the 95 wt % of glyphosate.

Example gyphosphate ammonium (%) Yield (%) 1 96.9 92.8 2 96.4 95.5 395.9 97.8 4 95.7 98.0 5 95.8 98.0 6 96.0 97.3 7 95.8 98.5 8 95.2 98.7 995.7 98.1 10 95.1 98.8 11 96.0 98.3 12 96.2 95.1 13 96.4 94.2 14 96.196.4 15 95.8 94.7 16 96.3 95.2 17 95.8 96.8 18 95.6 94.8 19 96.2 96.7

1. A process for preparing solid ammonium glyphosate by extraction withan organic solvent, which comprises adding glyphosate and water withoutaddition of an organic solvent into a normal reactor, introducinggaseous ammonia for the reaction to obtain an aqueous ammoniumglyphosate solution after the reaction is completed, characterized inthat, after the reaction is completed, an organic solvent is added intothe reaction solution, wherein said organic solvent has a relativelyhigh solubility in water or is miscible with water in any proportion,and the solid ammonium glyphosate is obtained by crystallizing andfiltering in suction.
 2. The process according to claim 1 wherein saidorganic solvent comprises an acetal, a monobasic alcohol having 1-4carbon atoms, or a mixture thereof.
 3. The process according to claim 2wherein said organic solvent comprises an acetal, or a monobasic alcoholhaving 1-4 carbon atoms.
 4. The process according to claim 2 or 3wherein said monobasic alcohol having 1-4 carbon atoms comprisesmethanol, ethanol propanol or n-butanol, and said acetal comprisesmethylal.
 5. The process according to claim 1 wherein the added organicsolvent to water content in the reaction solution has a weight ratio of1:1-10:1.
 6. The process according to claim 1 wherein the added organicsolvent to water content in the reaction solution has a weight ratio of2:1-5:1.
 7. The process according to claim 1 wherein said glyphosate isan undried powder having a water content of 5-20%, or a dry powderhaving a glyphosate content more than 90% by weight, and the glyphosateto water added in the reactor has a weight ratio of 0.2-2:1.
 8. Theprocess according to claim 1 wherein the ammonia to the glyphosate addedto the reactor has a mole ratio of 1.01:1-1.5:1.
 9. The processaccording to claim 1 wherein the reaction is carried out under atemperature of 30-100° C. and at the completion of the reaction, thereaction solution has a pH of 5-8.
 10. The process according to claim 1wherein the solid ammonium glyphosate obtained from filtration isfurther dried to make the water and organic solvent contained thereindecreased to less than 0.1-2%.
 11. The process according to claim 1wherein a mother liquor is collected after the filtration which containsthe organic solvent, is separated by rectification or distillation, andthe organic solvent is returned for use in the crystallization, and theaqueous solution containing ammonium glyphosate is returned back to thereaction process.
 12. The process according to claim 1 wherein theaqueous solution containing ammonium glyphosate is used for preparingthe aqueous formulation of ammonium glyphosate salt.